xref: /openbmc/linux/include/linux/int_log.h (revision 9ab04d7e)
1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
2 /*
3  * Provides fixed-point logarithm operations.
4  *
5  * Copyright (C) 2006 Christoph Pfister (christophpfister@gmail.com)
6  */
7 
8 #ifndef __LINUX_INT_LOG_H
9 #define __LINUX_INT_LOG_H
10 
11 #include <linux/types.h>
12 
13 /**
14  * intlog2 - computes log2 of a value; the result is shifted left by 24 bits
15  *
16  * @value: The value (must be != 0)
17  *
18  * to use rational values you can use the following method:
19  *
20  *   intlog2(value) = intlog2(value * 2^x) - x * 2^24
21  *
22  * Some usecase examples:
23  *
24  *	intlog2(8) will give 3 << 24 = 3 * 2^24
25  *
26  *	intlog2(9) will give 3 << 24 + ... = 3.16... * 2^24
27  *
28  *	intlog2(1.5) = intlog2(3) - 2^24 = 0.584... * 2^24
29  *
30  *
31  * return: log2(value) * 2^24
32  */
33 extern unsigned int intlog2(u32 value);
34 
35 /**
36  * intlog10 - computes log10 of a value; the result is shifted left by 24 bits
37  *
38  * @value: The value (must be != 0)
39  *
40  * to use rational values you can use the following method:
41  *
42  *   intlog10(value) = intlog10(value * 10^x) - x * 2^24
43  *
44  * An usecase example:
45  *
46  *	intlog10(1000) will give 3 << 24 = 3 * 2^24
47  *
48  *   due to the implementation intlog10(1000) might be not exactly 3 * 2^24
49  *
50  * look at intlog2 for similar examples
51  *
52  * return: log10(value) * 2^24
53  */
54 extern unsigned int intlog10(u32 value);
55 
56 #endif
57